Well, it could be defective if you managed to damage it on removal or something, but if it was working fine when you pulled it out and you think you were careful with it, it is likely a cooling issue on his side. However, if he knows what he is doing (suggested by having at least 1 additional cooler), he is probably installing it right and the chip may have been damaged at some point, on your end or his.
I really don't know ,I sold him motherboard + CPU and CPU wasn't taken out by me during the shipping process I figured its best to leave CPU in its socket so it would avoid bent pins .These are his words in the email ....
This is important. Today I went to the Computer shop and give my processor to check. Then They check with high quality heat sink(copper plated)+ artic silver thermal paste and Asus motherboard. Then power on the pc. Oh god it was started with no errors. Then we visited to the bios and check cpu temp. OMG ! It's passing above 95C. Then they said some seriously damage with cpu. They charged $5 testing
I said earlier I had sold my pc to buy your components. How can I solve this? Please help me"
I am curious as to why he had the PC shop check it first... would make me possibly wonder if he messed it up himself. Your sure it was working fine when you dissembled it?
When he received my package he assembled the components himself and told me CPU is bad (powering off) ,then I said to him take it to a computer shop/technician to test the system in the hands of a professional and which he did. And to answer your second question : Basically I was using those components till the last moment I shipped the components. So yes CPU was working perfectly.
It is certainly possible he damaged some component then, he could have used a crappy PSU, not taken care to avoid static discharge, did not correctly apply thermal paste, etc... I understand it is too late, but to avoid liability on issues like this, you could CYA by taking pictures or video or something before/while you disassemble and package the product. Personally it does not sound like it is your fault, and this seems like a lot to take but it could save future headaches. I am sure as an individual you did not provide any kind of warranty but if you sold it through a site they may have some kind of policy, it just makes it easier when you can say/show "This is how it was working before I disassembled, it was taken apart carefully, and properly packaged, beyond this it is either you (the buyer) or the shipper who is responsible".